Table 1.

Brain networks with relevance to IBS

Network	Core regions and inputs	Key features
Default mode network	Medial prefrontal cortex, posterior cingulate or retrosplenial cortex, inferior parietal cortex, lateral temporal cortex and hippocampal formation179,180	Comprised of brain regions whose activity is greater during rest than goal-directed task performance181 Associated with self-related processing, including monitoring internal thoughts and future planning179,182,183
Emotional arousal network	Amygdala, its positive connections with the locus coeruleus complex and inhibitory feedback projections to the amygdala from prefrontal and anterior cingulate subregions, and from the hippocampus	Activated by perceived or real perturbation of the organism’s homeostasis Generates rapid feedback inhibition of amygdala,184–186 thereby limiting the magnitude and duration of network activity and related activity in the central autonomic network
Central autonomic network	Control centres in the pontine-medulla (including PAG and hypothalamus), the central nucleus of the amygdala, and several cortical regions (including the anterior INS, ACC, prefrontal and motor regions)187,188	Regions related to SNS control overlap with the executive-processing and salience-processing networks (including the ventral anterior INS), whereas regions related to parasympathetic control are more associated with the default mode network154 Provides central control and modulation of the ANS Involved in regulating respiratory, cardiovascular, endocrine and digestive system activity during cognitive, affective and motor tasks and sensation
Sensorimotor network	Core cortical regions are primary somatosensory cortex (S1, post central gyrus), primary motor cortex (M1; precentral gyrus), secondary somatosensory cortex (S2) and supplemental motor area189 Close connections exist between the posterior INS (primary interoceptive cortex) and S1 Sensorimotor network connectivity to the thalamus, which relays peripheral sensory information to the cortex,190 is established by 2 years of age191	Receives sensory input from the periphery and is important for awareness of body sensations and generation of appropriate motor responses Primary and secondary motor cortex, through their projections to the central autonomic network, might have a modulatory role in the sympathetic control of visceral function192
Central executive network	Lateral prefrontal cortices and posterior parietal cortex193	Activated during tasks involving executive functions such as attention, working memory, planning and response selection Often coactivated with regions of the salience network,39 as the brain attempts to focus its limited processing capacity to only salient information via attention, working memory, planning and response selection193
Salience network	Dorsal ACC and anterior INS Core regions have strong connections to medial prefrontal and temporal regions, and subcortical regions including the amygdala, PAG and basal ganglia194–196 Dorsal portions of the anterior INS receives prefrontal input, whilst ventral portions are closely linked with the amygdala and emotional arousal system	Anterior INS can be considered the main hub in the brain, switching from default mode network to activity-related networks, and coordinating and adjusting bodily and behavioural responses to environmental changes Responds to subjective salience of any interoceptive and exteroceptive stimulus reaching the brain, or to the expectation of such stimuli, and coordinates appropriate attentional, behavioural, affective and visceral responses to such stimuli39,197 Responds with the most appropriate responses to biologically and cognitively relevant stimuli based on maintaining homeostasis193,194 regardless of whether the subject is awake, engaged in a particular task, or asleep (achieved through close salience network connections with the other networks)

Abbreviations: ACC, anterior cingulate cortex; ANS, autonomic nervous system; INS, insula; PAG, periaqueductal grey; SNS, sympathetic nervous system.